The present invention relates to a new and improved construction of a high-speed or rapid grounding device for metal encapsulated high-voltage switching installations comprising a grounding bolt which, upon igniting a propellent charge, can be forwardly shifted or otherwise displaced out of its rest position into its grounding or earthing position in order to electrically connect the capsule with a conductor encapsulated therein.
In the case of metal encapsulated high-voltage switching installations, especially those filled under pressure with SF.sub.6 (sulphur hexafluoride) as the insulating gas, it can happen that upon occurrence of arcs between the conductor and the capsule the resultant rapid heating and expansion of the gas can cause rupture of the capsule. Furthermore, if the arc burns for a sufficiently long time the installation can be otherwise damaged until destruction. In any event, a significant danger is present both for human beings and the installation and such danger must be obviated. In order to prevent bursting or rupture of the capsule or the like there was heretofore proposed an overpressure safety device employing rupture membranes or diaphragms. To extinguish the arcs there was strived for rapid cut-off of the current i.e., high-speed grounding. In those cases of the prior art relying upon the use of rupture or bursting membranes it was proposed for the purpose of controlling the switching operations to employ the pressure drop and/or the further inflow of gas from supply containers in order to trigger the switching operations. Yet, with these prior art proposals there had to be accepted quite considerable time-delays, so that due to further burning of the arc the installation was heavily damaged. Moreover, owing to bursting or rupture of the membrane or diaphragm there had to be accepted at least a partial loss of the gas fill. Additionally, there could not be attained an effective complete protection of the operating personnel.
There has also been proposed in this art, in addition to the use of rupture or bursting membranes, to rely upon the increased current, which arises upon the presence of arcs, for triggering switching operations. If, however, the total current remains within the rated current range, then, notwithstanding the presence of arcs no switching operation takes place. Even if the rated current is exceeded response of the switch is nonetheless critical inasmuch as its response time inherently cannot be so short that a switching operation already occurs in the presence of brief overcurrent surges. Hence, the switching operation occurs at such a large point in time that it is not possible to effectively prevent damage to the installation because of arc formation. It has also already been proposed to incorporate into the installation reference arc locations at which the arc destructs a rupture or bursting membrane and there is strived for an immediate or instantaneous extinguishing of the arc in that the one electrode is distanced from the other electrode by the outflowing gas. The cutting-off or grounding of the installation is undertaken in the already described manner, that is to say, with a time-delay. Moreover, it is really questionable whether there can actually occur in this way an extinguishing of the arc. Additionally, there is not eliminated the drawback that gas flows out of the installation.